| The key target of the study in orogenic belt is to properly reconstruct their three-dimension architecture and uncover their evolution. Though orogenic belts are varied, and different orogenic belts have different mechanisms, evolutions and three-dimension architectures, all orogenic belts have experienced strong tectonic migration and mixing, which are called non-Smithization .The orogenic strata have following characteristics: During the subduction (obduction) and intracontinental orogeny, the strata experienced dramatic tectonic migration and mixing, resulting in various tectonic features. A short sequence usually composed of tectonic slices of various origins, times, deformations and metamorphisms, and scales. The original sequence was badly destroyed. The extant fragments of orogenic belt usually took form as melanges, especially the accretion complex wedge generated in subduction zone, which is contrary to the Law of Superposition. The original location of the accretion is also contradicted with the Law of Original Horizonality, because the accretion is oblique with high degree. Marine rocks, volcanic rocks of continental margin and metamorphic rocks were well-developed in the orogenic belt, especially ultra-basic, basic rocks were wide spread and were intensely metamorphosed, accompanied by metamorphic slices returned from hundred kilometers underground with ultra-high pressure and magma movements during syn-orogeny and post-orogeny, thus formed the colorful landscapes. During the non-Smithization, the orogenic belt became the integration of mixed materials, and the traditional Smith methods are no longer fit the need of the study and practice in orogenic belt. How to carry out detail study in orogenic belt need prompt solution. Thus urged us to change our old thoughts and turn to non-Smith stratigraphy for help to reconstruct and restore the architecture, component and evolution of orogenic belt, and it will enhance Chinese level on geological research and environmental surveying and appraisal.The studied area located at the junction of Eastern Kunlun and West Qinling, and the Qaidam Plate and the South China Plate. Its ocean—continent transitions underwent Proterozoic, Early Paleozoic and Late Paleozoic—Early Mesozoic cycles, so the strata, sediments and structures are rather complex. There lied two ophiolite melange belts of different ages in Eastern Kunlun Orogenic Belt, i.e., middle-south Eastern Kunlun compound ophiolite belt in the north, A'nimaqing ophiolite melange belt in the south, which stands for two sutures of different ages. All these favor the study on the components, architectures and evolutions of the orogenic belt, and further on the Qinling—Kunlun orogenic belt and on the evolution of the south and north plates of West China.Based on lots of field work (21 surveyed melange sections, totally 160 km, 1 640 km mapping route of 1∶250 000 geologic map), indoors assays and referring former researcher's results, following conclusions are summarized.1.The conception, studied objects and basic constituents of non-Smith strata are elaborated from theory level: Non-Smithian strata are the strata that have undergone mixing of different degrees, thus were deformed, metamorphosed and displaced into disorder totally or partially. They are the disorder parts in orogenic belts. Melange is the solo studied object of non- Smithian stratigraphy. The slices (blocks) in melange is one of the basic constituents of non- Smithian strata, and also one of the basic units in the non-Smithian mapping. The slices used in this paper refer to blocks divided by small-scale tectonic boundaries and have certain constitutes. Superslices used in this paper refer to a set of slice association with similar tectonic deformation bounded by large-scale tectonic mixing.2. Guided by non-Wilson cycle theory generalized by Yin et al. (1998), the forming of non- Smithian strata are expounded at theory level. The paleo-oceans in orogenic belts were rather complex, especially the oceans in Chinese paleo-Tethys, most were archipelagos, which were broad (up to several latitudes) and unclean, with many archipelagos, a mosaic of seas and lands including rifted blocks and valleys, seaways, microplates and micro-oceans, and island arcs, seamount and marginal seas. The archipelagic oceans experienced polystage opening, closing and soft-collision during its ocean-basin transitions, so the strata in orogenic belt devolved from non-Wilson cycle usually underwent polystages strong tectonic mixings, inducing the geologic bodies of various episodes, stages of the same episodes, tectonic facies, paleogeographic units and tectonic levels patching and non-sequence imbricating one another in short distance.3. A set of systematic theory pertaining to the setting, division, terms, defining principles and practice were put forward:"four-dimension splitting-converging model of tectonic slices"and"material, age, facies, location and process of deformation and metamorphism"analysis method. 1∶250 000 Dongi Conag melange region are divided into two belts, two sub-belts, and 14 superslices, which are further divided into 15 slices according to their lithology, and are analyzed for"constituents, age, facies, location and process of deformation and metamorphism".4. Important advance are made in the date of slices and superslices: (1) Abundant acritarch and a few radiolarian fossils are collected in the"barren strata"formed by epi-middle metamorphic slices at Gouli, Longshigenggongwu, thus provide data evidence for this set of strata. A series of isotopic dating data (14) showed that the date are between 1 000 Ma and 500 Ma, close to that of the fossils. (2) Amaranth radiolarian silicate close connected with ophiolite slices are discovered in"Ma'erzheng Fm."along Huashxia—Long Stone Hill for the first time, and abyssal Early Permian radiolarians are got, thus provide important reference date for the forming age of ophiolite in this belt. (3) The slices constituting Buqingshan ophiolite melange belt are detailed studied on biostratigraphy, getting abundant foraminifers, fusulinida, coral, spongiaria, calcareous algae, sporopollen and trace fossils. The geologic age, paleoecology and paleoenvironment of the relative slices (blocks) are discussed from biotic standpoint for the first time. The detail biotic features of the melange provide abundant and detail data for the understanding of the forming of A'nimaqing orogenic belt.5. Based on thorough study on the east part of Eastern Kunlun Orogenic belt, a valuable try by using tectonic facies to analyze non- Smithian strata are took. Dominated by the evolution time of the orogenic belt, according to the paleogeographic units, basins and formation occurred in different stages and locations, the tectonic facies of 1∶250 000 Dongi Conag sheet are divided into 7 facies types and 21 facies. The forming, constituent and evolution of the east part of Eastern Kunlun orogenic belt are detail uncovered by using tectonic theory and method.6. Pre-Jinning—Indo-sinian polystage ocean-continent transitions and the forming of non-Smith strata are studied. Our study show that the ophiolites in the fault were the products of polycycle dispersal and convergence, and there existed at least three periods, i.e., Middle Proterozoic, Caledonian and Hercynian. The melange belt occurred not only near the fault, but the whole south part of the Eastern Kunlun, which is the integration of mixed materials formed by tectonic slices of different origins, stages and deformations. The tectonic melange are interfingered by slices of different stages, so come the name"Compound Melange Belt of the South Kunlun", which can be subdivided into northern ophiolite melange belt and southern melange belt according to the lithology of the basements and the evolution. The northern ophiolite melange belt contains various ophiolites of different times, and at least experienced three ocean-continent cycles, i.e., pre-Jinning cycle, Jinning—Caledonian cycle and Hercynian —Indo-sinian cycle. The structure and evolution of the south tectonic melange are relative simple, and its basement, Middle Proterozoic metamorphosed diorite (Kuhai complex), is relative younger. Kuhai complex is remarkable different from the northern Baishahe Gr. or Xiaomiao Gr. in metalithology, so it is an isolated block. The outer of the basement are active Early Carboniferous-Middle Permian sediments. The Late Paleozoic sediment areas are related to the Hercynian A'nimaqing ocean in genesis, and both are branch troughs. Upper Permian—Middle Triassic (including Gequ Fm., Hongshuichuan Gr. and Naochangjiangou Fm.), which are representatives of foreland accumulation after collision, angular contacting the underlying strata. It seemed the south tectonic melange has only undergone the Hercynian—Indo-sinian ocean—continent transition from the sedimentary formation, but a few Caledonian syntectonic granites are found in the basement, which showed the Caledonian movement has also left some traces in this subzone. The A'nimaqing Melange consists of Buqingshan—Huashxia superslice, Manite superslice and allochthonous nappe superslice. The A'nimaqing Melange bordered the south melange belt on the north with the NWW South Kunlun Fault extending along Dongi Conag Lake—Hongshuichuan—Alag Lake, and the Bayan Har block on the south with NWW Long Stone Hill Fault. The Buqingshan—Huashxia superslice is complex, including Middle Proterozoic diorite-facies Kuhai melange slice, ophiolite slice of different times, Early Permian—Early Triassic flysch wedge, basic-acid volcanic slice and carbonate slice and Late Triassic—Early Jurassic Yangqu Fm. terrestrial clastic slice. The ophiolites can be divided into two groups at least; one lies in the Kuhai complex and intersected by Caledonian island granite, which may be attributed to Caledonian or pre-Caledonian ophiolite association; the other lies in the Early Permian—Early Triassic Ma'erzheng Fm. of Buqingshan Gr., including ultramafic rock, basalt, diabase dike and pelagic siliceous-argillaceous association, and Early Permian radiolarian are found in the silicates, which reflect that the time is Hercynian. Manite superslice is relative simple, dominated by the flysch wedge, ophiolite, carbonate slice of Ma'erzheng Fm. of Buqingshan Gr., lacking deep metamorphosed slice. The fossils in the two slices show mixture of Permian and Triassic, but the pelagic silicate in the Buqingshan—Huashxia slice dated as Early Permian, so the associated ophiolite should be Early Permian. So the Buqingshan—Huashxia superslice developed a little earlier than the Manite slice, and the zoned ophiolite in them may due to the southward retrogression subduction, accretion and mixing.One important attribution of International Stratigraphic Guide lies in that it encourages the study on the multiple classification and correlation of the strata. The strata can be divided into as many kinds as the dividing standards, though the dividing limits are not consistent. Like other branches of stratigraphy (evento-, geneto-, econo-, tectono- and sequence stratigraphy, and so on) appeared successively in recent twenty years, non- Smithian stratigraphy is aimed to deeply demonstrate the characteristics of various melanges in the orogenic belt from four-dimension splitting-converging of tectonic slices. Obviously, the standpoint of this new branch is different from that of the other branches, yet their aims are the same, which is to demonstrate the colorful features of the strata. Therefore, non-Smithian stratigraphy is not excluding the other branches, but an important supplement for them, especially for the tectonostratigraphy. They are twin sister branches, and they are the two keys to uncover the disorder or partially order strata in the orogenic belt. Tectonostratigraphy emphasize on the analysis of the patterns and episodes of the deformation, while non-Smithian strata stressing on understanding of the constituent, original time, environment, paleo-tectonic settings and process of deformation and metamorphism of various slices through the four-dimension splitting-converging of the tectonic slices.
|
PDF Full Text Request